1. Field of the Invention
The present invention relates to a cutting insert, and more particularly to a cutting insert capable of enhancing the surface finish of worked materials and lengthening the durability of a cutting tool which has utilized in conjunction with the cutting insert, capable of efficiently removing cut chips from the cutting region by making a chip breaker into a complete non uniform curved surface to flow the cut chips in the most natural direction and curling, which are formed when performing a desired cutting operation, to also minimize the resistance to chip flow and the occurrence of the adhesion phenomenon.
2. Description of the Related Art
The machine industry such as the automotive industry etc. has been well developed heretofore, and thereby a variety of manufacturing processes have been automatized and performed at high speed. As a result, there exists a need for enhancing the performance of the cutting tool and for lengthening the durability of the cutting tool which has been well utilized in the machine industry.
The cutting tool is mainly used to cut ferrous or nonferrous metals under the state that it is mounted in a machine tool. The processes of cutting the metals using the cutting tool can be classified into two ways. According to the first way, the cutting tool cuts a metal workpiece under the state that an edge of cutting tool is brought into contact with a surface of the metal workpiece when rotating the workpiece, According to the second way, a cutting insert having a cutting edge cuts a metal workpiece, which is fixed at a predetermined position on a work station, when rotating the cutting insert under the state that the cutting insert is mounted in a machine tool using a holder for cutting tool.
The cutting insert is used to cut the workpiece under the state that it is mounted to a portion of the cutting tool directly contacting with the workpiece. The cutting insert is the most important factor in a metal cutting process. Further, the quality and the shape of the cutting insert is the most important factor for determining the durability of the cutting tool and the quality of the worked materials.
However, in the metal cutting process using the cutting insert, it is the most important things that metal chips generated from the workpiece, in the form of chip, when cutting unessential portions of the workpiece are securely and effectively flowed from the cutting region. Accordingly, a variety of endeavors for developing a cutting insert capable of securely flowing the metal chips from the cutting region without interfering with the continuing cutting process and without endangering the operating personnel have been proposed.
As a part of the endeavors, a method of changing the shape of the cutting insert for effectively cutting the workpiece has been proposed. Generally, the cutting insert has a rake surface and a flank surface. The rake surface allows the cut chips for flowing. An angle and a shape of the rake surface play an important role in determining the durability of the cutting insert, the surface finish of worked materials, a chip breaking, cut chip flowing and a cutting resistance, etc. The specific shape of the sloping surface and the surplus surface is called as "chip breaker". Chip breakers having a variety of shapes have been developed heretofore in the field of the art with respect to manufacturing the cutting insert. A standard of developing the chip breaker in relation to the shape thereof is the quality of the workpiece, the shape of the workpiece, a size of the cut portion of the workpiece, a precision of the cutting process, the quality of the cutting tool, etc.
However, according to the prior art, since a predetermined angle is present between a rake surface and a certain plane, a unnatural cutting phenomenon, which is not associated with a natural cutting mechanism proceed in the metal cutting process, can be generated. Due to this phenomenon, the cutting resistance is increased when cutting the workpiece. Further, the workpiece can be melted and stuck to the cutting edge of the cutting tool at the time that the workpiece begins to be melt. In addition, there are many problems such that the badness of the chip breaking, the excess wear of the cutting tool, the chipping of the cutting edge, the breakdown of the cutting tool, etc.
FIG. 11A is a top view of a cutting insert according to the prior art, and FIG. 11B is a sectional view taken along the line XI--XI of FIG. 11A.
Referring to FIGS. 11A and 11B, a cutting insert 10 according to the prior art includes a main body 12 having substantially parallel an upper surface 11 and a bottom surface 13. A circle opening 18 is formed through the center of the main body 12. Circle opening 18 provides a means whereby a holder for cutting tool (not shown) can be fitted into circle opening 18 to secure cutting insert 10 to the holder for cutting tool.
Cutting insert 10 includes four cutting corners 15. Two cutting edges 16 and two chip grooves 17 adjacent to the cutting edges 16 extend from cutting corners 15. Cutting edges 16 extend from cutting corners 15 to the middle portion of cutting edges 16 at a predetermined angle. Cutting edges 16 comprise a straight sloping portion 16a and a horizontal center portion 16b, respectively.
Straight sloping portions 16a of cutting edges 16 vary in width, widening from cutting corners 15 to the middle portion of cutting edges 16.
Chip grooves 17 continuously extend across sections of cutting corners 15 and sections adjacent to straight sloping portions 16a. Chip grooves 17 are provided with sloping side surfaces 17a,17b. Sloping side surfaces 17a,17b uniformly maintain in width at the center portions 16b of cutting edges 16. Sloping side surfaces 17a,17b and upper surface 11 of cutting insert 10 form an angle greater than 130.degree..
Upper surface 11 includes a flat horizontal section 11a and flat triangular sections 11b. Flat triangular sections 11b form a predetermined angle with flat horizontal section 11a. Flat horizontal section 11a meets with sloping side surfaces 17a,17b of chip grooves 17 in an adjoining relationship and accordingly form an angle therebetween. The altitude of flat horizontal section 11a is lower than that of cutting edge 16.
However, in cutting insert 10 as described above, sloping side surfaces 17a,17b of the chip breaker allowing the cut chips to flow there through are plane in figure. Further, the common junctures between flat horizontal section 11a and flat triangular sections 11b, sloping side surface 17a and flat triangular section 11b, sloping side surface 17b and flat horizontal section 11a, etc. form an angle therebetween. Accordingly, the cut scraps produced during the metal cutting process undergo compulsive bending stresses while passing through the planes such as sloping side surfaces 17a,17b and the common junctures. As a result, the irregular and excess stresses can be applied to cutting edge 16 playing an important role in the cutting process, and thereby the cut chips are melted and stuck to cutting edge 16. Further, the cut chips cannot smoothly and securely flowed from the cutting region, and the surface finish of worked materials is not good. In addition, the chipping of the cutting edge can be generated. Consequently, the cutting tool has a short life.
U.S. Pat. No. 5,772,366 issued to Jorgen Wiman et al on Jun. 30, 1998 discloses a cutting insert having an integral chip control surface. In this patent, the cutting insert comprises a compound body consisting of a sintered cemented carbide substrate with a surface coating which is a diamond coating with a thickness of 1.about.20 .mu.m deposited directly from a gas phase in a reactor by CVD or PVD technique. Therefore, it is necessary to perform any post-processing for a plurality of curved projections and an integral chipformer provided on an upper surface of the cutting insert.
However, in the Wiman al.'s invention, since a central portion of an upper surface of the cutting insert is perpendicular to acute-angled corners of the cutting insert, there is no chip breakers in a direction parallel with a corner cutting edge. Accordingly, the resistance to chip flow is relatively high. Since an acute-angled angle is in existence at the juncture between the central portion and a sloping flank on the upper surface of the cutting insert, the cutting resistance to the cutting edges is increased and therefore the built-up edge phenomenon frequently generates at the cutting edges. If a workpiece to be cut has a sharp-shaped outer surface, the separation of the thin film of the workpiece can be generated on the outer surface and thereby the surface finish of the workpiece is not good. Consequently, it is impossible to maintain pointed cutting edges during the workpiece of aluminum cutting process.